Solar System Phenomena — Mercury in 2020

The path of Mercury against the background stars in 2020

The upper chart shows the path of Mercury across the background stars over the course of the year. Stars to magnitude +4.5 are shown with some fainter objects included to complete constellation patterns. The white circles represent the planet on the first day of the month and are scaled according to apparent magnitude. The faint paths before the first circle and after the last circle represent the planet's positions in December of last year and January of next. In general, the planet moves from right to left except when it's in retrograde and proceding in the opposite direction. As an inferior planet, Mercury never strays far from the Sun so it always begins and ends the year near the constellation of Sagittarius, located about one quarter of the way in from the left side of the chart.

The lower charts show how the appearance of Mercury changes over the year. Below each image is listed the date, the apparent magnitude, the apparent diameter of the disk (in arc-seconds), the geocentric distance (in au), the elongation from the Sun (in degrees) and the percentage of the disk which is illuminated. Like the Moon, Mercury exhibits a complete range of phases, from new to crescent to gibbous to full and back again. Because its synodic period is around four months, Mercury completes this phase cycle three times each year. Note how Mercury's magnitude varies widely, ranging (approximately) from −2.0 to +6.0 between conjunctions.

Mercury begins the year as a morning sky object but immediately disappears from view. Three more morning apparitions occur in 2020, with the March–April appearance an excellent one for equatorial and southern hemisphere observers and the end-of-year apparition favouring northern temperate latitudes. Mercury also appears in the west after sunset four times this year. The late spring appearance in May and June is the best chance for planet chasers in the north to see this object in the evening whilst late August through October yields splendid observing opportunities for viewers in southern latitudes.

01 Januaryelongation 5.8°, illuminated fraction 99.1%, magnitude −0.9, disk diameter 4.7 arc-seconds
02 Januaryplanetary conjunction: 1.5° south of Jupiter
10 Januarysuperior conjunction
12 Januaryplanetary conjunction: 2.0° south of Saturn
16 JanuarySagittariusCapricornus
25 January1.3° north of the Moon
01 Februaryelongation 14.5°, illuminated fraction 84.8%, magnitude −1.0, disk diameter 5.6 arc-seconds
07 Februaryascending node
10 Februarygreatest elongation east: 18.2°
12 Februaryperihelion
16 Februarystationary point: direct → retrograde
26 Februaryinferior conjunction
01 Marchelongation 8.8°, illuminated fraction 3.5%, magnitude +3.6, disk diameter 10.6 arc-seconds
07 MarchAquariusCapricornus
09 Marchstationary point: retrograde → direct
10 MarchCapricornusAquarius
16 Marchdescending node
24 Marchgreatest elongation west: 27.8°
27 Marchaphelion
01 Aprilelongation 26.5°, illuminated fraction 63.5%, magnitude +0.1, disk diameter 6.6 arc-seconds
04 Aprilplanetary conjunction: 1.3° south of Neptune
09 AprilAquariusPisces
15 AprilPiscesCetus
18 AprilCetusPisces
28 AprilPiscesAries
01 Mayelongation 4.6°, illuminated fraction 98.5%, magnitude −1.7, disk diameter 5.0 arc-seconds
planetary conjunction: 0.3° south of Uranus
04 Maysuperior conjunction: anti-transit
05 Mayascending node
09 MayAriesTaurus
10 Mayperihelion
22 Mayplanetary conjunction: 0.9° south of Venus
24 May2.8° north of the Moon
27 Maymaximum declination north
29 MayTaurusGemini
01 Juneelongation 23.2°, illuminated fraction 44.7%, magnitude +0.3, disk diameter 7.5 arc-seconds
04 Junegreatest elongation east: 23.6°
12 Junedescending node
17 Junestationary point: direct → retrograde
23 Juneaphelion
01 Julyelongation 4.4°, illuminated fraction 0.0%, magnitude +6.2, disk diameter 11.9 arc-seconds
inferior conjunction
12 Julystationary point: retrograde → direct
22 Julygreatest elongation west: 20.1°
01 Augustelongation 16.6°, illuminated fraction 69.6%, magnitude −0.8, disk diameter 6.1 arc-seconds
ascending node
04 AugustGeminiCancer
06 Augustperihelion
14 AugustCancerLeo
17 Augustsuperior conjunction
19 August2.8° south of the Moon
01 Septemberelongation 13.0°, illuminated fraction 92.2%, magnitude −0.7, disk diameter 5.0 arc-seconds
02 SeptemberLeoVirgo
08 Septemberdescending node
19 Septemberaphelion
22 September0.3° north of Spica
01 Octoberelongation 25.8°, illuminated fraction 61.1%, magnitude +0.1, disk diameter 6.7 arc-seconds
greatest elongation east: 25.8°
07 OctoberVirgoLibra
14 Octoberstationary point: direct → retrograde
20 OctoberLibraVirgo
25 Octoberinferior conjunction
28 Octoberascending node
01 Novemberelongation 12.5°, illuminated fraction 14.0%, magnitude +1.5, disk diameter 8.9 arc-seconds
02 Novemberperihelion
03 Novemberstationary point: retrograde → direct
10 Novembergreatest elongation west: 19.1°
13 November1.7° south of the Moon
16 NovemberVirgoLibra
01 Decemberelongation 10.6°, illuminated fraction 95.5%, magnitude −0.8, disk diameter 4.9 arc-seconds
03 DecemberLibraScorpius
05 Decemberdescending node
06 DecemberScorpiusOphiuchus
14 Decemberlunar occultation: 1.0° south of the Moon
18 DecemberOphiuchusSagittarius
20 Decembersuperior conjunction
24 Decembermaximum declination south

Because the orbits of the planets are tilted slightly to the plane of the ecliptic, a planet normally passes to the north or the south of the Sun at conjunction. However, if the planet is near a node (the place in the orbit where the planet crosses the ecliptic) when it reaches conjunction, the planet may appear to cross in front of or behind the disk of the Sun. This situation occurs in May when Mercury actually passes behind the Sun from the vantage point of Earth. This type of conjunction is sometimes called an anti-transit or secondary eclipse.

The superior conjunction of Mercury in May 2020


The dates, times and circumstances of all planetary and lunar phenomena were calculated from the JPL DE406 solar system ephemeris using the same rigorous methods that are employed in the compilation of publications such as The Astronomical Almanac.